Antibody ligation of CD9 in stromal cell cocultures blocks spontaneous differentiation of a multipotential stem cell line. EML-C1 cells were analyzed by flow cytometry before and after coculture for 7 days on MS-5 stromal cells along with 1 μg/mL KMC8.8 or an IgG2a isotype-matched control antibody. Cells were harvested and stained with PE-labeled Sca-1, PE-labeled CD45RA, PE-labeled TER119, FITC-labeled Mac1 (shaded histograms). Control staining obtained with isotype-matched antibody is also shown (open histograms). These are representative results from one of three similar experiments.